Electric Vehicle Extended Range Hybrid Battery Pack System

ABSTRACT

A power source comprised of a first battery pack (e.g., a non-metal-air battery pack) and a second battery pack (e.g., a metal-air battery pack) is provided, wherein the second battery pack is only used as required by the state-of-charge (SOC) of the first battery pack or as a result of the user selecting an extended range mode of operation. Minimizing use of the second battery pack prevents it from undergoing unnecessary, and potentially lifetime limiting, charge cycles. The second battery pack may be used to charge the first battery pack or used in combination with the first battery pack to supply operational power to the electric vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of the filing date of U.S. ProvisionalPatent Application Ser. No. 61/372,351, filed Aug. 10, 2010, thedisclosure of which is incorporated herein by reference for any and allpurposes.

FIELD OF THE INVENTION

The present invention relates generally to batteries and, moreparticularly, to means for optimizing the power source of an electricvehicle that utilizes battery packs of differing types.

BACKGROUND OF THE INVENTION

A metal-air cell is a type of battery that utilizes the same energystorage principles as a more conventional cell such as a lithium ion,nickel metal hydride, nickel cadmium, or other cell type. Unlike suchconventional cells, however, a metal-air cell utilizes oxygen as one ofthe electrodes, typically passing the oxygen through a porous metalelectrode. The exact nature of the reaction that occurs in a metal-airbattery depends upon the metal used in the anode and the composition ofthe electrolyte. Exemplary metals used in the construction of the anodeinclude zinc, aluminum, magnesium, iron, lithium and vanadium. Thecathode in such cells is typically fabricated from a porous structurewith the necessary catalytic properties for the oxygen reaction. Asuitable electrolyte, such as potassium hydroxide in the case of azinc-air battery, provides the necessary ionic conductivity between theelectrodes while a separator prevents short circuits between the batteryelectrodes.

Due to the use of oxygen as one of the reactants, metal-air cells havesome rather unique properties. For example, since the oxygen does notneed to be packaged within the cell, a metal-air cell typically exhibitsa much higher capacity-to-volume, or capacity-to-weight, ratio thanother cell types making them an ideal candidate for weight sensitiveapplications or those requiring high energy densities.

While metal-air cells offer a number of advantages over a conventionalrechargeable battery, most notably their extremely high energy density,such cells also have a number of drawbacks. For example, care must betaken to avoid the undesired evaporation of electrolyte, especially inhigh temperature, low humidity environments. It is also necessary toensure that there is a sufficient supply of air to the cells duringdischarge cycles, and means for handling the oxygen emitted from thecells during the charge cycles. Another potential disadvantage of ametal-air cell is the power available on discharge. Due to the kineticsof the electrode reactions, the maximum discharge rate is far lower thanthat of many other types of cells, such as lithium-ion cells.

Accordingly, while metal-air cells offer some intriguing benefits, suchas their high energy densities, their shortcomings must be taken intoaccount in order to successfully integrate the cells into a system. Thepresent invention provides such a system by combining a metal-airbattery pack with a conventional battery pack in order to gain thebenefits associated with each battery type.

SUMMARY OF THE INVENTION

The present invention provides a power source comprised of a firstbattery pack (e.g., a non-metal-air battery pack) and a second batterypack (e.g., a metal-air battery pack), wherein the second battery packis only used as required by the state-of-charge (SOC) of the firstbattery pack or as a result of the user selecting an extended range modeof operation. Minimizing use of the second battery pack prevents it fromundergoing unnecessary, and potentially lifetime limiting, chargecycles. The second battery pack may be used to charge the first batterypack or used in combination with the first battery pack to supplyoperational power to the electric vehicle.

In at least one embodiment of the invention, a method of extendingdriving range of an electric vehicle is provided, the electric vehicleincluding at least a first battery pack (e.g., non-metal-air batterypack) and a second battery pack (e.g., metal-air battery pack), themethod including the steps of (i) determining the SOC of the firstbattery pack; (ii) comparing the current SOC of the first battery packto a first preset minimum SOC to determine whether the first batterypack needs immediate charging or may be used to power the electricvehicle; and (iii) comparing the current SOC of the first battery packto a second preset minimum SOC, wherein if the current SOC of the firstbattery pack is less than the second preset minimum SOC the secondbattery pack is used to charge the first battery pack. After charging ofthe first battery pack by the second battery pack has been initiated,for example due to the first battery pack requiring immediate charging,the method may further comprise the step of comparing the current SOC ofthe first battery pack to the first preset minimum SOC to determine whenthe SOC of the first battery pack has increased sufficiently to allow itto be used to supply power to the electric vehicle. After charging ofthe first battery pack by the second battery pack has been initiated,the method may further comprise the step of comparing the current SOC ofthe first battery pack to a preset maximum SOC to determine when the SOCof the first battery pack has increased sufficiently to allow chargingto be terminated. Prior to charging the first battery pack with thesecond battery pack, the method may further comprise the step ofcomparing the current SOC of the second battery pack to a third presetminimum SOC, wherein use of the second battery pack to charge the firstbattery pack is only allowed if the current SOC of the second batterypack is greater than the third preset minimum SOC. The method mayfurther comprise comparing the current SOCs of both the first and secondbattery packs to preset minimums to determine when vehicle operationmust be terminated.

In at least one embodiment of the invention, a method of extendingdriving range of an electric vehicle is provided, the electric vehicleincluding at least a first battery pack (e.g., non-metal-air batterypack) and a second battery pack (e.g., metal-air battery pack), themethod including the steps of providing means for selecting between anormal mode of operation and an extended range mode of operation,wherein when the extended range mode is selected vehicle operationalpower is provided by the first battery pack and the second battery packis used to charge the first battery pack, and wherein when the normalmode is selected vehicle operational power is provided by the firstbattery pack and the second battery pack is not used. The means forselecting between modes may be integrated within the vehicle's userinterface or navigation system. When the normal mode of operation isselected, the method may further include the steps of (i) determiningthe SOC of the first battery pack; and (ii) comparing the current SOC ofthe first battery pack to a first preset minimum SOC, wherein if thecurrent SOC of the first battery pack is less than the first presetminimum SOC the second battery pack is used to charge the first batterypack. When the normal mode of operation is selected, the method mayfurther include the steps of (i) determining the SOC of the firstbattery pack; (ii) comparing the current SOC of the first battery packto a first preset minimum SOC to determine whether the first batterypack needs immediate charging; and (iii) comparing the current SOC ofthe first battery pack to a second preset minimum SOC, wherein if thecurrent SOC of the first battery pack is less than the second presetminimum SOC the second battery pack is used to charge the first batterypack. Prior to charging the first battery pack with the second batterypack, the method may further comprise the step of comparing the currentSOC of the second battery pack to a preset minimum SOC, wherein use ofthe second battery pack to charge the first battery pack is only allowedif the current SOC of the second battery pack is greater than the presetminimum SOC. The method may further comprise comparing the current SOCsof both the first and second battery packs to preset minimums todetermine when vehicle operation must be terminated.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the primary components of an electric vehicle thatutilizes both a metal-air battery pack and a conventional battery pack;

FIG. 2 illustrates the basic methodology of the invention;

FIG. 3 illustrates the methodology of a preferred embodiment;

FIG. 4 illustrates the methodology of an alternate embodiment;

FIG. 5 illustrates a modification of the methodology of FIG. 3;

FIG. 6 illustrates a modification of the methodology of FIG. 4;

FIG. 7 illustrates a methodology based on the processes shown in FIGS. 3and 5; and

FIG. 8 illustrates a methodology based on the processes shown in FIGS. 4and 6.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably. The term “battery pack” as used hereinrefers to one or more individual batteries that are electricallyinterconnected to achieve the desired voltage and capacity for aparticular application, the individual batteries typically containedwithin a single piece or multi-piece housing. The terms “power system”and “battery system” may be used interchangeably and as used hereinrefer to an electrical energy storage system that has the capability tobe charged and discharged such as a battery or battery pack. The term“electric vehicle” as used herein refers to either an all-electricvehicle, also referred to as an EV, plug-in hybrid vehicles, alsoreferred to as a PHEV, or a hybrid vehicle (HEV), a hybrid vehicleutilizing multiple propulsion sources one of which is an electric drivesystem. It should be understood that identical element symbols used onmultiple figures refer to the same component, or components of equalfunctionality. Additionally, the accompanying figures are only meant toillustrate, not limit, the scope of the invention and should not beconsidered to be to scale.

Given the high energy density and the large capacity-to-weight ratiooffered by metal-air cells, they are well suited for use in electricvehicles. Due to their limited power density, however, their use is mostappropriate when combined with a more conventional power source, such asa lithium ion battery pack. This aspect is illustrated in FIG. 1 whichshows the primary components of an EV 100 that utilizes both a metal-airbattery pack 101 and a conventional, non-metal-air battery pack 103. Asused herein, metal-air batteries refer to any cell that utilizes oxygenas one of the electrodes and metal (e.g., zinc, aluminum, magnesium,iron, lithium, vanadium, etc.) in the construction of the otherelectrode. Conventional battery pack 103 utilizes non-metal-air cells,and preferably ones that provide high power density, thus providing acombined power source that achieves an optimal combination of energy andpower. Exemplary batteries used in conventional battery pack 103include, but are not limited to, lithium ion (e.g., lithium ironphosphate, lithium cobalt oxide, other lithium metal oxides, etc.),lithium ion polymer, nickel metal hydride, nickel cadmium, nickelhydrogen, nickel zinc, silver zinc, etc. In a preferred application,battery packs 101 and 103 are coupled to one or more drive motors 105that provide propulsion to one or more wheels of EV 100. A controller107 optimizes the vehicle's hybrid power source, i.e., battery packs 101and 103, in light of the current battery pack conditions (e.g.,state-of-charge, temperature, etc.), preferred battery packcharge/discharge conditions (e.g., state-of-charge, temperature range,etc.), and the various operating conditions. Exemplary operatingconditions include those placed on the system by the user (e.g., speed,acceleration, etc.), road conditions (e.g., uphill, downhill, etc.),charging system (e.g., available power, available time for charging,etc.), and environmental conditions (e.g., ambient temperature,humidity, etc.).

FIG. 2 illustrates the basic methodology of the invention. As shown,during the discharge cycle 201 one or both battery packs 101 and 103provide energy to the intended application (e.g., propulsion, cooling,auxiliary systems, etc.), the flow of energy represented by paths203/204. Similarly, during the charging cycle 205 one or both batterypacks 101 and 103 receive energy from a charging source, not shown, theflow of energy represented by paths 207/208. The charging source may bean external power source (e.g., power grid) or an internal power source(e.g., regenerative system). Lastly, in some embodiments energy may betransferred directly between battery packs 101 and 103 as represented byenergy flow pathway 209.

In accordance with the invention, and as illustrated in system 200,controller 107 controls the flow of energy to and from both themetal-air battery pack 101 and the non-metal-air battery pack 103. Asdescribed in detail below, the methodology applied by controller 107 isbased on the input from a variety of sensors 211 as well as the currentoperating conditions (e.g., temperature and state-of-charge (SOC), etc.)of both battery packs.

The primary advantage of using two different types of battery packs, andmore specifically, a metal-air battery pack 101 and a conventional,non-metal-air battery pack 103, is that the operational characteristicsof the two battery types are quite different. As a result, an EVutilizing both battery types can be designed to take advantage of thebenefits of both battery types, while significantly limiting thenegative effects of either type.

While the specific operating requirements and characteristics of the twobattery packs will depend upon the particular chemistries of the cellsselected for each battery pack, the basic differences between the twotypes are provided below, thus further clarifying how the presentinvention utilizes both battery types to optimize operation of thecombined power source.

Energy Density—The energy density of the metal-air cells is very high,even relative to high density non-metal-air cells such as lithium-ioncells. In general, this is the result of the metal-air cells utilizingoxygen, contained within the air, as one of the reactants, thus reducingcell weight and increasing energy density. Accordingly, in weightsensitive applications such as EVs, metal-air cells offer a distinctadvantage over non-metal-air cells in terms of energy density.

Power Density—The power density of a cell is determined by the cell'sreaction kinetics. Currently the chemistries, materials andconfigurations used in metal-air cells provide a lower power densitythan that achieved by many non-metal-air cells. While the lower powerdensity is adequate for many applications, it is lower than desired formore demanding applications. As a result, by combining both cell typesin a single application as presently described, the high energy density,moderate power density metal-air cells can provide a baseline powersource while the moderate energy density, high power densitynon-metal-air cells can provide the necessary power for peak loads, forexample the loads that may be experienced during acceleration, highspeed, and hill climbing. Clearly the relative sizes allocated for eachbattery type/pack within an EV depends upon the configuration and designof the vehicle (i.e., vehicle weight, performance goals, etc.).

Optimal Charge/Discharge Temperatures—Temperature affects many criticalcharacteristics of battery operation regardless of the batterytype/chemistry. Exemplary characteristics affected by temperatureinclude cell voltage and discharge capacity, cell impedance, cell life,non-recoverable capacity loss (at high temperatures), and chargingefficiency. While the preferred and optimal charge and dischargecharacteristics depend upon the particular cell design, chemistry, andreaction kinetics, in general metal-air cells may be charged anddischarged at lower temperatures than non-metal-air cells without undulyaffecting cell life and efficiency.

State-of-Charge (SOC)—The depth of discharge reached during thedischarge cycle, and the level that a cell is charged (up to 100 %)during the charge cycle, may dramatically affect the performance andlife characteristics of a cell. These characteristics are dependent uponcell design and chemistry.

Recharge Characteristics—By definition a rechargeable battery isrechargeable, however, the number of times that a cell may be rechargedwithout substantially affecting the capabilities and lifetime of thecell vary greatly with cell design and chemistry. In general, however,current state-of-the-art metal-air cells are not capable of beingrecharged as many times as a non-metal-air cell without causing asignificant degradation in lifetime and capacity.

As noted above, the capabilities and lifetime of a rechargeable batteryare both affected by the number of times that the cell is charged (i.e.,charge cycles). Accordingly, in a preferred embodiment of the invention,the dual battery pack arrangement is used to reduce the number of timesone, or both, battery packs are charged. As current metal-air batteriesare more susceptible to the effects of repeated charge cycles, thepresent embodiment illustrates the use of the invention to minimize thecharge cycles of the metal-air cells relative to the charge cycles ofthe non-metal-air cells. It should be understood, however, that theinvention may also be used to minimize the charge cycles of thenon-metal-air cells relative to the metal-air cells if, for example, atsome point the non-metal-air cells become more susceptible to theeffects of charging than the metal-air cells.

FIG. 3 illustrates a preferred embodiment of the invention utilizing afirst battery pack comprised of non-metal-air cell(s) and a secondbattery pack comprised of metal-air cell(s). As shown, once vehicleoperation is initiated (step 301), the state-of-charge (SOC) ofnon-metal-air battery pack 103 is determined (step 303). Note that inthe figures “non-metal-air” is abbreviated as “NMA” and “metal-air” isabbreviated as “MA”. Next, in step 305, it is determined whether or notthe current SOC is greater than a first preset SOC minimum(SOC_(NMA-Min1)). Preferably the first preset SOC minimum is set at theabsolute minimum SOC that the non-metal-air battery pack is allowed toreach. Typically this minimum is selected to prevent irreparable damageto the non-metal-air battery pack (e.g., 10% SOC, 5% SOC, 0% SOC or someother value). As long as the SOC of the non-metal-air pack is above thisminimum (step 307), then the non-metal-air pack 103 is used to provideoperational power to the vehicle (step 309), thus not draining themetal-air battery pack.

At step 311, the current SOC for the non-metal-air battery pack iscompared to a second preset minimum SOC (SOC_(NMA-Min2)). Preferably thesecond preset minimum is not the minimum allowable SOC for thenon-metal-air battery pack, rather the second preset minimum is set at alevel to ensure that vehicle performance is not affected while providingsufficient time to take advantage of the vehicle having a second batterypack, i.e., metal-air battery pack 101. For example, in one embodimentthe second preset minimum is set at 50% SOC; alternately, the presetminimum is set at 40% SOC; alternately, the preset minimum is set at 30%SOC; alternately, the preset minimum is set at 20% SOC. Other presetminimums may be used. If the current SOC is greater than the secondpreset (step 313), then the EV continues to utilize only the firstbattery pack, e.g., non-metal-air battery pack 103, to provide power tothe drive system and the other vehicle subsystems.

During step 311, if controller 107 determines that the current SOC ofbattery pack 103 is not greater than the second preset minimum (step315), then the current SOC of metal-air battery pack 101 is determined(step 317) and compared to a third preset minimum SOC, i.e.,SOC_(MA-Min) (step 319). Preferably the third preset minimum is set atthe absolute minimum SOC that the metal-air battery pack is allowed toreach. Typically this minimum is selected to prevent irreparable damageto the metal-air battery pack (e.g., 10% SOC, 5% SOC, 0% SOC or someother value). As long as the SOC of the metal-air pack is above thisminimum (step 321), then the metal-air battery pack is used to chargethe non-metal-air battery pack 103 (step 323).

At step 325, the current SOC of the non-metal-air battery pack is onceagain compared to the first preset minimum SOC. As long as the currentSOC is greater than the first preset minimum, the non-metal-air batterypack is used to supply operational power to the EV (step 327). If thenon-metal-air battery pack was already being used to power the EV (e.g.,via step 309), then in step 327 utilization of this battery packcontinues.

Next the current SOC of the non-metal-air battery pack is compared to apreset maximum SOC (step 329). Preferably the preset maximum is not themaximum allowable SOC for the non-metal-air battery pack, rather thepreset maximum is the value for the non-metal-air SOC at which chargingfrom the metal-air pack is preferably terminated. For example, in oneembodiment the preset maximum is set at 90% SOC; alternately, the presetmaximum is set at 80% SOC; alternately, the preset maximum is set at 70%SOC; alternately, the preset maximum is set at 60% SOC. Other presetmaximums may be used.

If controller 107 determines that the current SOC for the non-metal-airbattery pack is less than the preset maximum (step 331), charging of thenon-metal-air battery pack from the metal-air battery pack continues. Ifcontroller 107 determines that the current SOC for the non-metal-airbattery pack is greater than the preset maximum (step 333), charging isterminated (step 335) and vehicle operation continues with only thefirst battery pack providing operational power to the vehicle.

At step 319, if the current SOC of the metal-air battery pack fallsbelow the third preset minimum SOC, i.e., SOC_(MA-Min) (step 337),charging is terminated (step 339). Even with the SOC of the metal-airbattery pack falling below the third preset minimum SOC, operation ofthe vehicle may continue as long as the SOC of the non-metal-air batterypack remains greater than the first preset minimum SOC (step 341). Ifthe SOC of the non-metal-air battery pack falls below the first presetminimum SOC (step 343), then vehicle operation must be terminated (step345). It will be understood that the termination of vehicle operationwill follow a predefined procedure that may, for example, include lowpower warnings, gradual reduction in power (e.g., decreased accelerationand top speed), shut-down of non-essential vehicle systems (e.g., radioand interior lighting) prior to shutting down essential vehicle systems,etc.

In the embodiment described above and illustrated in FIG. 3, the secondbattery pack (e.g., the metal-air battery pack) is used to charge thefirst battery pack (e.g., the non-metal-air battery pack) when the SOCof the first battery pack falls below a preset value. In an alternateembodiment illustrated in FIG. 4, when the SOC of the first battery packfalls below the preset minimum (step 315), the second battery pack(e.g., metal-air battery pack 101) is used to augment the output fromthe non-metal-air battery pack (step 401), assuming that the SOC of themetal-air battery pack is greater than the preset minimum SOC asdetermined in step 319. By augmenting the output from the first batterypack, less drain is placed on it, thereby extending how long the firstbattery pack may be used prior to reaching its minimum acceptable SOC.At the same time, as the second pack (e.g., metal-air battery pack 103)is only used when the SOC of the first battery pack falls below a presetminimum, the second pack is protected from undergoing unnecessary chargecycles.

In the embodiment illustrated in FIG. 4, once the current SOC of thenon-metal-air battery pack exceeds the preset maximum (step 333) or whenthe current SOC of the metal-air battery pack falls below the thirdpreset minimum (step 337), use of the metal-air battery pack to augmentthe output of the non-metal-air battery pack is terminated asillustrated in steps 403 and 405, respectively.

In the embodiments illustrated in FIGS. 3 and 4 and described above, thesecond battery pack, typically the metal-air battery pack, is only usedwhen the SOC of the first battery pack, typically the non-metal-airbattery pack, falls below a preset SOC value. As a result, the secondbattery pack, typically the metal-air battery pack, is spared fromunnecessary charge cycles. FIGS. 5 and 6 illustrate modifications of theembodiments illustrated in FIGS. 3 and 4, respectively, in which whetheror not the second battery pack is used depends upon a selection made bythe user (e.g., driver). More specifically, vehicle 100 includes meansfor selecting a particular mode of operation, accessible by the user,which allows the user to select between at least two modes of operation;a normal range mode and an extended range mode. The mode selector isintegrated into the vehicle's user interface, for example using atouch-sensitive screen or some form of switch (e.g., toggle switch, pushbutton switch, slide switch, rotating selector switch, etc.).Alternately, the mode selection may be made in response to a selectionmade by the user, for example, by the user setting a destination in thenavigation system that falls outside of the vehicle's normal drivingrange, but within the vehicle's extended driving range. Accordingly, itwill be appreciated that the invention is not limited to a specificmeans of selecting the operational mode of the vehicle.

As shown in FIG. 5, once vehicle operation is initiated (step 301) thesystem determines whether or not the extended range mode has beenselected (step 501). As previously noted, the extended range mode may bemade using a mode selector or in response to another selection made bythe driver (e.g., destination entered into the navigation system). Ifthe extended range has not been selected (step 503), then the firstbattery pack is used to supply all operational power to the vehicle,thereby sparing the second battery pack from unnecessary use, andtherefore unnecessary charging cycles. Based on the currentstate-of-the-art, the first battery pack is a conventional (i.e.,non-metal-air) battery pack and the second battery pack is a metal-airbattery pack. This choice is based on the achievable power density foreach type of cell, as well as the demonstrated sensitivity of each celltype to repeated charge/discharge cycles.

If the normal range is selected, either via active selection or bydefault, then the non-metal-air battery pack 103 is used to supply powerfor all of the operational needs of the vehicle (step 505). If theextended range is selected (step 507), then the non-metal-air batterypack is used to supply power to the vehicle (step 509) and the metal-airbattery pack is used to charge the non-metal-air battery pack (step511), thereby maintaining the non-metal-air battery pack within apreferred SOC range and extending its capabilities, and thus thevehicle's range. Alternately, and as illustrated in FIG. 6 and describedabove relative to FIG. 4, when the extended range is selected (step 507)the metal-air battery pack is used to augment the output of thenon-metal-air battery pack (step 601), thereby extending the vehicle'srange.

In an alternate embodiment, the ability to select a particularoperational mode (e.g., normal versus extended range) is combined withthe ability for the system to react to the SOC of the first battery packfalling below a preset minimum. This combination of features allows theuser to pre-select an operational mode, and for the system to alteroperation based on the user's actual needs. Thus, for example, if a userselects the normal operating mode based on the expected driving range,but then unexpectedly exceeds the normal range, the system automaticallyextends the driving range utilizing the second power source. FIG. 7illustrates a preferred embodiment of this configuration, theillustrated system including the attributes of the processes shown inFIGS. 3 and 5. Similarly, the system illustrated in FIG. 8 combines theattributes of the processes shown in FIGS. 4 and 6.

It will be appreciated that while the illustrated embodiments arepreferred, a variety of minor variations are envisioned that are clearlywithin the scope of the invention. For example, the process illustratedin FIG. 8 assumes that the capacity of the first battery pack, i.e., thenon-metal-air battery pack, is larger than that of the second batterypack, i.e., the metal-air battery pack. As a result, in this embodimentthe SOC of the metal-air battery pack is expected to fall below itsminimum allowable SOC before the non-metal-air battery pack falls belowits minimum allowable SOC. Clearly the invention is not limited to thisconfiguration.

Additionally, while both the metal-air battery pack 101 and thenon-metal-air battery pack 103 are shown and described as singularpacks, it should be understood that one or both of these packs may becomprised of multiple modules, and that the present invention is equallyapplicable to such a configuration. The use of multiple modules (ormini-battery packs) may be useful in distributing weight throughout EV100, or to fit into the physical constraints of the EV's chassis/body,and does not impact the present invention.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. For example, while theillustrated embodiments assume the use of a non-metal-air battery packas the first battery pack and a metal-air battery pack as the secondbattery pack, these battery types may be reversed, thus using themetal-air battery pack as the first battery pack and the non-metal-airbattery pack as the second battery pack. Accordingly, the disclosuresand descriptions herein are intended to be illustrative, but notlimiting, of the scope of the invention which is set forth in thefollowing claims.

What is claimed is:
 1. A method of extending driving range of anelectric vehicle, the electric vehicle including at least a firstbattery pack and a second battery pack, wherein the first and secondbattery packs are comprised of different battery types, the methodcomprising the steps of: a) determining a current state-of-charge (SOC)of the first battery pack; b) comparing said current SOC of the firstbattery pack with a first preset minimum SOC, wherein if said currentSOC of the first battery pack is less than said first preset minimum SOCsaid method skips to step d), and wherein if said current SOC of thefirst battery pack is greater than said first preset minimum SOC,vehicle operational power is supplied to the electric vehicle from thefirst battery pack; c) comparing said current SOC of the first batterypack with a second preset minimum SOC, wherein said second presetminimum SOC is greater than said first preset minimum SOC, wherein ifsaid current SOC of the first battery pack is greater than said secondpreset minimum SOC said method returns to step a), and wherein if saidcurrent SOC of the first battery pack is less than said second presetminimum SOC said method further comprises the step of: d) charging thefirst battery pack from the second battery pack.
 2. The method of claim1, wherein after step d) said method further comprises the steps of: e)comparing said current SOC of the first battery pack with said firstpreset minimum SOC, wherein if said current SOC of the first batterypack is less than said first preset minimum SOC said method returns tostep d), and wherein if said current SOC of the first battery pack isgreater than said first preset minimum SOC, vehicle operational power issupplied to the electric vehicle from the first battery pack.
 3. Themethod of claim 2, wherein after step e) said method further comprisesthe steps of: f) comparing said current SOC of the first battery packwith a preset maximum SOC, wherein if said current SOC of the firstbattery pack is less than said preset maximum SOC said method returns tostep d), and wherein if said current SOC of the first battery pack isgreater than said preset maximum SOC, first battery pack charging isterminated and said method returns to step a).
 4. The method of claim 1,wherein after step d) said method further comprises the steps of: e)comparing said current SOC of the first battery pack with a presetmaximum SOC, wherein if said current SOC of the first battery pack isless than said preset maximum SOC said method returns to step d), andwherein if said current SOC of the first battery pack is greater thansaid preset maximum SOC, first battery pack charging is terminated andsaid method returns to step a).
 5. The method of claim 1, wherein priorto step d) said method further comprises the steps of: c2) determining acurrent SOC of the second battery pack; c3) comparing said current SOCof the second battery pack with a third preset minimum SOC, wherein ifsaid current SOC of the second battery pack is greater than said thirdpreset minimum SOC said method continues to step d), and wherein if saidcurrent SOC of the second battery pack is less than said third presetminimum SOC said method further comprises the steps of: i) comparingsaid current SOC of the first battery pack with said first presetminimum SOC, wherein if said current SOC of the first battery pack isgreater than said first preset minimum SOC said method returns to stepa), and wherein if said current SOC of the first battery pack is lessthan said first preset minimum SOC said method further comprises thestep of terminating vehicle operation.
 6. The method of claim 5, whereinin step b) if said current SOC of the first battery pack is less thansaid first preset minimum SOC said method skips to step c2), and whereinin step c) if said current SOC of the first battery pack is less thansaid second preset minimum SOC said method skips to step c2).
 7. Themethod of claim 5, wherein after step d) said method further comprisesthe steps of: e) comparing said current SOC of said first battery packwith said first preset minimum SOC, wherein if said current SOC of saidfirst battery pack is less than said first preset minimum SOC saidmethod returns to step c2), and wherein if said current SOC of saidfirst battery pack is greater than said first preset minimum SOC,vehicle operational power is supplied from said first battery pack tosaid electric vehicle.
 8. The method of claim 7, wherein after step e)said method further comprises the steps of: f) comparing said currentSOC of the first battery pack with a preset maximum SOC, wherein if saidcurrent SOC of the first battery pack is less than said preset maximumSOC said method returns to step c2), and wherein if said current SOC ofthe first battery pack is greater than said preset maximum SOC, firstbattery pack charging is terminated and said method returns to step a).9. The method of claim 5, wherein after step d) said method furthercomprises the steps of: e) comparing said current SOC of the firstbattery pack with a preset maximum SOC, wherein if said current SOC ofthe first battery pack is less than said preset maximum SOC said methodreturns to step c2), and wherein if said current SOC of the firstbattery pack is greater than said preset maximum SOC, first battery packcharging is terminated and said method returns to step a).
 10. Themethod of claim 1, wherein said first battery pack is comprised of aplurality of non-metal-air cells and said second battery pack iscomprised of a plurality of metal-air cells.
 11. A method of extendingdriving range of an electric vehicle, the electric vehicle including atleast a first battery pack and a second battery pack, wherein the firstand second battery packs are comprised of different battery types, themethod comprising the steps of: providing means for selecting between anormal mode of operation and an extended range mode of operation;wherein when said extended range mode of operation is selected, themethod further comprises the steps of supplying vehicle operationalpower to the electric vehicle from the first battery pack and chargingthe first battery pack from the second battery pack; and wherein whensaid normal mode of operation is selected, the method further comprisesthe steps of supplying vehicle operational power to the electric vehiclefrom the first battery pack and not charging the first battery pack fromthe second battery pack.
 12. The method of claim 11, wherein said firstbattery pack is comprised of a plurality of non-metal-air cells and saidsecond battery pack is comprised of a plurality of metal-air cells. 13.The method of claim 11, wherein said means for selecting between saidnormal mode of operation and said extended range mode of operation isintegrated within a user interface corresponding to said electricvehicle.
 14. The method of claim 11, wherein said means for selectingbetween said normal mode of operation and said extended range mode ofoperation is integrated within a navigation system corresponding to saidelectric vehicle.
 15. The method of claim 11, wherein when said normalmode of operation is selected, the method further comprises the steps:a) determining a current state-of-charge (SOC) of the first batterypack; b) comparing said current SOC of the first battery pack with afirst preset minimum SOC, wherein if said current SOC of the firstbattery pack is greater than said first preset minimum SOC said methodreturns to step a), and wherein if said current SOC of the first batterypack is less than said first preset minimum SOC said method furthercomprises the step of: c) charging the first battery pack from thesecond battery pack.
 16. The method of claim 15, wherein prior to stepb) said method further comprises the steps of: a2) comparing saidcurrent SOC of the first battery pack with a second preset minimum SOC,wherein said first preset minimum SOC is greater than said second presetminimum SOC, wherein if said current SOC of the first battery pack isless than said second preset minimum SOC said method skips to step c),and wherein if said current SOC of the first battery pack is greaterthan said second preset minimum SOC said method performs step b). 17.The method of claim 15, wherein prior to step c) said method furthercomprises the steps of: b2) determining a current SOC of the secondbattery pack; b3) comparing said current SOC of the second battery packwith a second preset minimum SOC, wherein if said current SOC of thesecond battery pack is greater than said second preset minimum SOC saidmethod continues to step c), and wherein if said current SOC of thesecond battery pack is less than said second preset minimum SOC saidmethod further comprises the steps of: i) comparing said current SOC ofthe first battery pack with a second preset minimum SOC, wherein saidfirst preset minimum SOC is greater than said second preset minimum SOC,wherein if said current SOC of the first battery pack is greater thansaid second preset minimum SOC said method returns to step a), andwherein if said current SOC of the first battery pack is less than saidsecond preset minimum SOC said method further comprises the step ofterminating vehicle operation.
 18. The method of claim 11, wherein whensaid extended range mode of operation is selected, the method furthercomprises the steps: a) determining a current SOC of the second batterypack; b) comparing said current SOC of the second battery pack with afirst preset minimum SOC, wherein if said current SOC of the secondbattery pack is greater than said first preset minimum SOC, charging ofthe first battery pack by the second battery pack continues, and whereinif said current SOC of the second battery pack is less than said firstpreset minimum SOC said method further comprises the steps of: c)terminating charging of the first battery pack by the second batterypack; d) determining a current SOC of the first battery pack; e)comparing said current SOC of the first battery pack with a secondpreset minimum SOC, wherein if said current SOC of the first batterypack is greater than said second preset minimum SOC said method returnsto step a), and wherein if said current SOC of the first battery pack isless than said second preset minimum SOC said method further comprisesthe step of terminating vehicle operation.